Disc drives of the “Winchester” and optical types are well-known in the industry. Such drives use rigid discs, which are coated with magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor, which causes the discs to spin and the surface of each disc to pass under a hydrodynamic bearing disc head slider. The slider typically carries a transducer, which writes information to and reads information from the disc surface. Typically, a single disc surface will have one disc head slider passing over the surface.
In a conventional disc drive, multiple discs are coupled to and rotate about a spindle. Each of the discs has two substantially flat surfaces that are capable of storing data. Typically these discs are stacked in a parallel relationship with each other. The sliders are designed to move within the space between the adjacent discs while flying in close proximity the disc surface. The slider is coupled to the distal end of a thin, arm-like structure called a head suspension assembly (HSA), which is inserted within the space between two adjacent discs.
The track accessing arm moves a slider or group of sliders from track to track across the surfaces of the disc. The track accessing arm typically includes a head gimbal assembly, a load beam, an actuation component to move the track accessing arm, and a read/write head and slider supported by the head gimbal assembly. The load beam provides a load force which encourages the slider towards the disc surface. A gimbal is positioned between the slider and the load beam, or is integrated into the load beam, and provides a resilient connection that allows the slider to pitch and roll while following the typography of the disc.
The slider typically includes a bearing surface which faces the disc surface. As the disc rotates, air is drug underneath the slider by the disc and along the bearing surface in a direction approximately parallel to the tangential velocity of the disc. As the air passes beneath the bearing surface, air compression along the air flow path causes the air pressure between the disc and the bearing surface to increase, which creates a hydrodynamic lifting force which counteracts the load force and causes the slider to lift or “fly” above or in close proximity to the disc surface.
One type of slider is a “self-loading” air-bearing slider, which includes a leading taper, a pair of raised side-rails, a cavity dam and a subambient pressurization cavity. The leading taper is typically lapped or etched onto the end of the slider that is opposite the read/write head. The leading taper pressurizes the air as the air is dragged under the slider by the disc surface. An additional effect of the leading taper is that the pressure distribution under the slider has a first peak near the tapered end or “leading edge” due to high compression angle of the taper step, and a second peak near the read/write head or “trailing edge” due to a low bearing clearance necessary for efficient magnet recording. This dual peak pressure distribution results in a bearing with a relatively high pitch stiffness.
The bearing clearance between the slider and the disc surface at the read/write head is an important parameter to disc drive performance. As average flying heights continue to be reduced, altitude induced and manufacturing variation induced fly height loss are an increasing source of head contact and modulation that lead to read/write failures. In addition, variation in slider shape (i.e. crown and cross curvature) also lead to unwanted head/disc contact.
Further, there is a tendency for the slider to change both its pitch angle and its fly height as the ambient air pressure around the disc surface changes as a result of altitude changes to the drive. This change in flying characteristics of the slider can result in the head crashing into the surface of the disc, causing damage to the information contained on the data surface. Prior art sliders have used lap pads or diamond-like carbon (DLC) pads to account for this change in fly height as well as to reduce the stiction force associated with the slider contacting the disc surface. A typical slider without pads is typically designed to fly at a pitch angle of approximately 160 micro radians. When the slider is fitted with pads, the slope of the pitch angle is increased to approximately 220 micro radians. This increased slope created by the pads results in a high pitch offset and an increased sensitivity to ambient pressure changes.
The flying characteristics of the slider are typically controlled by variations in the pressurization over the surface of the slider. A slider typically experiences areas of positive pressure and areas of negative pressure. The areas of positive pressure tend to cause the slider to rise above the surface of the disc. Whereas, areas of negative pressure tend to cause the slider to move towards the surface of the disc. By balancing these pressurization areas a slider designer is able to control the flying characteristics of the slider. Typically, disc sliders have a positive pressure area at the leading edge and at the trailing edge or near these regions. Some sliders also have a positive pressure area along the side edges. Sliders commonly have a cavity dam after the leading edge pressurization feature which creates an area negative pressure to help offset the positive pressure force generated by the leading edge feature, and to encourage the slider towards the disc surface while maintaining the designed pitch angle. However, when the altitude of a slider is increased, for example, by taking the drive up in an airplane, the pressure differential generated by these two areas of pressure is often not enough to maintain the designed flying characteristics. Therefore, a slider design is desired which minimizes the sensitivity of the slider to altitude.
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.